Ion implantation is a process by which dopants or impurities are introduced into a substrate via bombardment. In semiconductor manufacturing, the dopants are introduced to alter electrical, optical, or mechanical properties. For example, dopants may be introduced into an intrinsic semiconductor substrate to alter the type and level of conductivity of the substrate. In manufacturing an integrated circuit (IC), a precise doping profile is often important for proper IC performance. To achieve a desired doping profile, one or more dopants may be implanted in the form of ions in various doses and various energy levels.
Referring to FIG. 1, there is shown a conventional ion implantation system 100. As illustrated in the figure, the ion implantation system 100 may comprise an ion source and a complex series of beam-line components through which an ion beam 10 passes. The ion source may comprise an ion source chamber 102 where desired ions are generated. The ion source may also comprise a power source 101 and an extraction electrode 104 disposed near the ion source chamber 102. As illustrated in the figure, the extraction electrodes 104 may include a suppression electrode 104a and a ground electrode 104b. Each of the ion source chamber 102, the suppression electrode 104a, and the ground electrode 104b may include an aperture: the ion source chamber 102 may include an extraction aperture (not shown), the suppression electrode may include a suppression electrode aperture (not shown), and a ground electrode may include a ground electrode aperture (not shown). The apertures may be in communication with one another so as to allow the ions generated in the ion source chamber 102 may pass through, toward the beam-line components.
The beam-line components, meanwhile, may include, for example, a mass analyzer 106, a first acceleration or deceleration (A1 or D1) stage 108, a collimator 110, and a second acceleration or deceleration (A2 or D2) stage 112. Much like a series of optical lenses that manipulate a light beam, the beam-line components can filter, focus, and manipulate ions or ion beam 10 having desired species, shape, energy, and other qualities. The ion beam 10 that passes through the beam-line components may be directed toward a substrate 114 that is mounted on a platen 116 or clamp. The substrate 114 may be moved in one or more dimensions (e.g., translate, rotate, and tilt) by an apparatus, sometimes referred to as a “roplat.” It should be appreciated by those skilled in the art that the entire path traversed by the ion beam 10 is typically evacuated during ion implantation.
The ion source included in the ion implanter system 10 may be an indirectly heated cathode (IHC) source. In an IHC system, a cathode and a repeller electrode (or anti-cathode) may be positioned in the opposite sides of the ion source chamber 102. A filament may be positioned outside the ion source chamber 102 and in close proximity to the cathode in order to heat the cathode.
The ion source is required to generate a stable, well-defined ion beam 10 for a variety of different ion species and extraction voltages. In some embodiments, the temperature of the ion source, and particularly, the temperature of the ion source chamber 102, is important in determining the types of ions that are created and extracted. For example, when boron trifluorine (BF3) is used as a source or feed gas, it may become various ions, such as BF2+, BF+, or B+. It is the temperature within the ion source chamber 102 that is one of the factors in determining which of these ions is created. Larger molecular ions, such as BF2+ are more likely created at lower temperatures, while atomic ions, like B+ are more likely created at higher temperatures. Typically, the temperature of the ion source chamber 102 is either not regulated, or is controlled by varying or regulating the amount of energy or power that is passed through the filament and used to heat the cathode.
Higher levels of power may result in mono-atomic ions. Lower levels of power may result in larger or molecular ions. However, lower levels of energy also tend to decrease the amount of ions that are generated, thereby lowering the available beam current. For this reason, implants that require larger or molecular ions may take more time to process than those with smaller or atomic ions. In other words, power, which is responsible for determining beam current, can also be used to determine the ion species that are to be created.
It would therefore be desirable to operate the ion source chamber such that the ion beam current and the ion species that are generated could be independently controlled. It would also be beneficial if larger or molecular ions could be generated at higher powers and thus with greater ion beam currents.